In digital satellite and cable technology, source material, i.e. programs, in the form of a digital transport stream are often encrypted by the service provider using Conditional Access (CA). The CA key is provided to the end user, usually in the form of a chip or magnetic card or other means in the users system unit that allows reading of audio, video and data decryption keys within the transport stream. The CA key allows access to additional encryption keys within the transport stream. In order to provide trick-modes the source material must be decrypted and de-muxed in order to generate pointer files so the system unit can find specific portions of the source material and the source material itself stored for later play back. Trick-modes are defined infra. Generally, the source material is not stored “in the clear,” so it is encrypted before storage using a key provided by the system unit provider. An example of a system for accomplishing the aforementioned is illustrated in FIG. 1 and will now be described.
FIG. 1 is schematic diagram of a related art system for trick-mode play of audio/video streams. In FIG. 1 a system unit 100 includes a play section 105 and a trick-mode section 110. Play section 105 includes a transport stream decryptor 115, a transport stream demuxer 120, a system controller 125, a switch 130 (under the control of the system controller) and an audio/video (A/V) decoder and decompressor 135. Trick-mode section 110 includes a pointer file generator 140, a storage controller 145 under the control of system controller 125, a rescrambler 150, a storage medium 155 and a decrambler 160.
In operation, a transport stream is received by transport stream decryptor 115 and decrypted by the transport stream decryptor using a CA key provided by the service provider. Transport stream demuxer 120, demuxes the decrypted transport stream into an audio stream, a video stream and a data stream. The audio, video and data streams are then sent to switch 130, pointer file generator 140, and rescrambler 150. For real-time play, system controller 125 sets switch 130 to direct, when a mode signal 165 is set for real-time play, and the audio, video and data streams directed to A/V decoder and decompressor 135, which decompresses and decodes the signal components into a standardized format for display.
Rescrambler 150 encrypts the audio, video and data streams are encrypted using a key provided by the system unit manufacturer (not the CA key used by service provider to originally encrypt the transport stream) or a fixed encryption method not even requiring a key and saves the encrypted audio, video and data streams onto storage medium 155 a fixed encryption method not even requiring a key. Pointer generator 140 generates a trick-mode pointers from the decrypted transport stream and injects the trick-mode pointers into the encrypted audio, video and data streams stored on storage media 155. Descrambler 160 descrambles the stored streams using the key used by rescrambler 150, (again this is the key provided by the system unit manufacturer and not the key not the CA key used by service provider to originally encrypt the transport stream or a fixed decryption method not requiring a key) and passes the stored streams having trick-play pointers to A/V decoder and decompressor 135 when mode signal 165 sets switch 130 for play back.
Inherent with this type of system is the fact that the stored program is encrypted using a key provided by the system manufacturer not the service provider. Therefore, the service provider has effectively given up access control. This creates two problems, the first being, the service provider may object to giving up access control, and the second being the program encrypted by using a “local” key may be more susceptible to unauthorized access.